In the production of aluminum, it is customary to arrange the electrolyzers in a row at spaces between them, The electrolyzers in the row are connected in series, i.e. the cathode of each electrolyzer is connected through a bus system to the anode system of the next electrolyzer, so that electric current flows through the entire row of the electrolyzers.
In the course of operation of electrolyzers powerful electromagnetic fields are produced by heavy currents flowing through the electrolyzer elements, which substantially influence the process of aluminum electrolysis and the economical characteristics thereof.
With increased power of an aluminum-producing electrolyzer, adverse effect of the magnetic field upon the aluminum electrolysis process is increased. Interaction of the outer magnetic field with the currents flowing through the molten metal causes large-magnitude electromagnetic forces in the latter. These electromagnetic forces give rise to a distorted surface of the liquid cathode metal and to its vigorous circulation.
Considerable warping or buckling of the metal causes electrolyzers to operate at an electrode spacing exceeding the optimum one. This leads to an increase in the voltage across the pot, overexpenditure of electric power and overheating of the melt which adversely effects on the current yield.
As a result of vigorous circulation the molten metal is much more liable to entrapment in the near-the-anode space where it is oxidized by anode gases. Numerous observations have shown that in those zones of the electrolyzer wherein the magnetic field intensity and the level of circulating fluxes reach their peak values, the cathode casing wall deformation occurs and it is in these zones that the inside carbon plates of electrolyzers are most frequently destroyed by the molten metal.
Under the combined effect of gaseous fluxes and electromagnetic forces, waves arise on the surface of the fused aluminum which may result in local shorts that substantially reduce the current yield.
The exploitation of high-power electrolyzers may be economically warranted only if effective measures are developed to counteract the harmful effect of the magnetic field.
Several attempts have been initiated to overcome this disadvantage by modifying the method of current supply of the electrolyzers.
In one system of supplying current to aluminum-producing electrolyzers, the current conductors are split into several parallel buses to form a kind of horizontal plate below the electrolyzers, these conductors alternatively supplying current to the anodes. Although this configuration tends to suppress the magnetic fields, the large number of conductors necessitated interferes with operation of the potlines as well as occupying a good deal of space.
It has also been proposed to locate the current-supply buses at as great a distance from the electrolyzers as possible, while directing the current in adjacent conductors in opposing directions. Again, such an arrangement requires extensive housing and consequent large investment. Moreover, the extra length of the current-supply buses results in excessive power loss.
Investigations of the magnetic fields carried out in recent years both on mocked-up and industrial high amperage electrolyzers, have made it possible to visualise the requirements to the system of current-supply buses of an aluminum-producing electrolyzers, as may be expressed in the following formula: ##EQU1## where By denotes the cross component of the magnetic field,
Bx denotes the longitudinal component of the magnetic field, PA1 Bz denotes the vertical component of the magnetic field.
In other words, the afore-specified requirements imply the symmetry of the cross magnetic field, invariability of the values By and Bx along the axes of the electrolyzer and the requirement of minimum absolute values of Bz effective at the electrolyzer corners, as well as the symmetry of the vertical magnetic field with respect to the electrolyzer axes.
Widely known in the art is a system of current-supply buses for aluminum producing electrolyzers arranged in a row and spaced from each other, comprising cathode stacks, anode risers, and anode buses. In this system, the anode risers are arranged at the ends of the electrolyzer. Such a system of current-supply buses provides a symmetric magnetic field with a fair intensity value of its vertical component. The absolute values of the horizontal components of the magnetic field intensity, however, therewith tend to increase sharply, which results in a vigorous circulation of the molten aluminum in the electrolyzer, disturbed stability of the electrolysis process, and decreased engineering and economical factors.
The system of current-supply buses with the anode risers arranged at the ends of the electrolyzer involves a great proportion of aluminum buses expended on mounting and is characterized by a considerable voltage drop in the cathode stacks.
These disadvantages are eliminated in systems of current-supply buses having an arrangement of the anode risers different from that disclosed.
There is known a system of current-supply buses for aluminum-producing electrolyzers arranged transversely in a row and spaced from each other described in U.S. Pat. No. 3,415,724. This system comprises cathode stacks, anode risers aligned between the electrolyzers, and anode buses for supplying current to electrolyzer anode systems shaped as parallelograms, all the anode risers of each electrolyzer being arranged between the planes extending through the ends of the electrolyzer anode system. Flowing through the current-supply stacks of cathode buses, current is fed from the foregoing electrolyzer side located at the current inlet to the anode risers of the electrolyzer successive in the row, one part of the stacks being arranged under the bottom of the electrolyzer and the other part by-passed around the electrolyzer end portion.
This contributes to the symmetric distribution of all the three components of the magnetic field intensity and a drop in their absolute value, thereby providing stability of the electrolysis process and an increase in its engineering and economic factors.
The arrangement of the anode risers in the space between adjacent electrolyzers of a row cuts considerably the consumption of the aluminum current-supply buses and decreases power loss in the system of current-supply buses as compared with a system wherein the anode risers are arranged at the electrolyzer ends.
However, the presence of a group of the anode risers in the space between adjacent electrolyzers of a row and opposite the anode system interferes notably with mechanization of the handling of the electrolyzers, increases considerably the labor cost, the difficulties increasing as the number of the anode risers in the aforedescribed space increases. Attempts to decrease the number of the anode risers lead to a considerable increase of the magnetic field intensity values, which deteriorates the stability of the electrolysis process and decreases its engineering and economic factors.